1. Field of the Invention
The present invention relates to an assembly for tamping ballast supporting a track having rails, each rail having a gage side and a field side, the ballast tamping assembly being mounted on a machine frame of a track tamper and the machine frame being elongated in the direction of the track, the ballast tamping assembly comprising four independently displaceable ballast tamping units arrayed in a line extending transversely to the machine frame elongation, each ballast tamping unit comprising a carrier frame, a tamping tool carrier vertically adjustably mounted on the carrier frame, and a pair of vibratory tamping tools mounted on the tamping tool carrier for reciprocation in the track direction, each vibratory tamping tool having a tamping pick pivotal about an axis extending in the direction of the machine frame elongation and connected to a pivoting drive. Independently operable drives are connected to the ballast tamping units for displacing the ballast tamping units in a direction extending transversely to the machine frame elongation.
2. Description of the Prior Art
Such a ballast tamping assembly has been disclosed in U.S. Pat. No. 5,007,349, the four transversely independently displaceable ballast tamping units being mounted on a carrier which is rotatably mounted on the machine frame of a track tamper. Each ballast tamping unit has a pair of reciprocal vibratory tamping tools, and each tamping tool has two transversely adjacent tamping picks for immersion in the ballast alongside one of the rail sides. This arrangement makes the tamping pick positions more adaptable to the irregular track rail positions in track switches. In one embodiment of this ballast tamping assembly, all the tamping picks are transversely pivotal about axes extending in the direction of the machine frame elongation, and each tamping pick is connected to a pivoting drive. While this adds to the adaptability of the tamping pick positions to changing track rail positions, a proper positioning of the 16 pivotal tamping picks of the four ballast tamping units requires a disadvantageously long time and concentration by the operator during each tamping cycle.
Austrian patent No. 382,179 discloses a ballast tamping assembly with two independent ballast tamping units with one carrier frame and two tamping tool carriers independently vertically adjustably mounted thereon. Each tamping tool carrier has a pair of vibratory and reciprocatory tamping tools for immersion along the field side and the gage side of an associated rail, respectively. Each tamping tool has a tamping pick pivotal about an axis extending in the direction of the machine elongation. This enables any tamping pick to be pivoted out of the way of any obstacle encountered during tamping so that the tamping tools may be suitably immersed in the ballast even when such an obstacle is encountered. Such pivotal tamping picks are also disclosed in U.S. Pat. Nos. 3,534,687 and 4,537,135, and all these ballast tamping arrangements have the disadvantage that the distance between the four tamping units mounted on a common carrier frame is not variable for use under varying operating conditions.
British patent No. 2,201,178 discloses a ballast tamping assembly with four transversely independently displaceable ballast tamping units, the tamping picks of the tamping tools of each tamping unit being fixedly connected to the tamping tools. This prevents considerable portions of a track switch from being tamped, as is quite clear from FIG. 4 of the patent.
Austrian patent No. 378,386 discloses a ballast tamping assembly with two ballast tamping units whose carrier frame for a pair of reciprocable tamping tools is pivotal about an axis extending in the direction of the machine frame elongation so that the tamping tools may be consecutively immersed at the respective rail sides. Each tamping tool has two tamping picks one of which is pivotal about an axis extending in the direction of the machine frame elongation. This enables the pivotal tamping pick to be pivoted from a normal tamping position slightly spaced from the other tamping pick to another position wherein the tamping picks overlap. This reduces the effective immersion width of the tamping picks and enables the tamping unit to operate in relatively narrow tamping spaces, such as the point where a branch track branches off the main track. However, as FIG. 2 of the patent shows, at this point the ballast tamping unit must be consecutively centered, lowered and raised at each side of the rail for tamping.